Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
During a potential vehicular rollover event, one side of the wheels start lifting, and the roll center of the vehicle shifted to the contact patch of the remaining tires. This shifted roll center increases the roll inertia of moment of the vehicle, hence reduces the roll acceleration of the vehicle. However, the roll attitude could still increase rapidly. The corresponding roll motion when the vehicle starts side lifting deviates from the roll motion during normal driving condition. Therefore accurate characterization of the roll angle during potential rollover events is needed, since the feedback control for achieving rollover prevention is directly related to the vehicle roll angle. One way in which to determine roll angle is found in U.S. patent (application Ser. No. 10/091,264) entitled “Attitude Sensing System For An Automotive Vehicle Relative To The Road” filed Mar. 4, 2002. The system in that application is particularly suitable in situations where the four tires of a vehicle are contacting the road surface, i.e., when the vehicle does not have side lifting. However, the sensed relative roll angle in that system gets saturated due to various system limitations when the vehicle roll angle increases so as to cause side lifting although the actual relative roll angle of the vehicle is growing rapidly.
Many studies have been conducted for analyzing vehicular rollovers. There are many papers dealing with modeling roll dynamics when the vehicle has side lifting. In the reference “Modeling of rollover sequences,” (by Ralf Eger and Uwe Kiencke, Control Engineering Practice, vol. 11, pp 209–216, 2003) the rollover sequence during an impact is studied when the vehicle slides laterally into a rigid barrier. A multi-body rollover model with nonlinear suspensions is used. In order to simulate the vehicle rollover dynamics, the vehicle initial states right before impact, such as the vehicle lateral velocity, are required. In the paper “Dynamic Analysis Of Vehicle Rollover,” The 12th International Conference on Experimental Safety Vehicles, Goteborg, Sweden, May 29–Jun. 1, 1989, the rollover dynamics are studied for determining the influence of design parameters on the vehicle responses. In “Rollover Analysis Method Of A Large-Size Bus,” JSAE 9540020, 1995, by N. Niii, Y. Nishijima and K. Nakagawa, how to accurately simulate the rollover dynamics for a large bus is described.
Although the above-cited references help model and analyze the roll dynamics during potential rollover events, they have less practical application in active rollover control implementations. One reason is that the full car dynamics or detailed multi-body dynamics are too complicated to be implemented in feedback control algorithms. The second reason is that the initial condition or vehicle states right before the vehicular rollover are usually unknown and sometimes might not be able to be identified through the available sensor signals. Furthermore, certain variables used in the aforementioned analysis cannot be estimated by the available sensors.
It would therefore be desirable to provide a practical and implementation-ready system for determining the roll angle of the vehicle with respect to the road surface during potential rollover events.